The invention relates to a board element comprising a lightweight core and a cover layer of glass fiber-reinforced resin. In particular, the invention relates to a lightweight board element of high strength and stiffness. Such board elements find particular use in fabrication of table tennis tables, solar collectors, recreational vehicles, housing and other applications where strong, lightweight board members are used.
Lightweight board elements have been previously described. For instance, a lightweight board element is described in German Auslegeschrift No. 1,303,270. The core in that case comprises corrugated paper honeycomb.
There are no technical difficulties in production of non-warping weatherproof, decomposition-resistant board of this kind, if expense is of no importance. Technical problems arise only if the attempt is made to produce such board with the least possible use of material and using inexpensive materials. In composite construction, wherein a sandwich construction, a core of light inexpensive material is combined with cover layers of glass fiber-reinforced polyester resin, the problem is to minimize the proportion by weight of the relatively expensive covering layers.
Further, in respect to manufacturing cost, the board should be constructed in such a way that it will be possible to join the cover layers directly to the core in a single step before the cover layers harden and not in such a way that the prefabricated layers would have to be formed and subsequently bonded together. Finally, in the case of table tennis board, in addition to being weatherproof and true to form, the bounce of the ball on the board is important. Normally, light materials offer poor bouncing and playing properties.
In the case of solar collectors, on the other hand, it is essential that the absorbed thermal energy from the light rays not be lost by thermal conduction to the sub-structure. Board elements are needed therefore that are as rigid and stable as possible, and on the other hand, provide good insulation so that the absorbed thermal energy, instead of being carried off through the panel, will be efficiently taken up by the fluid used for heat transport, and carried off to be utilized.
It is therefore an object of the invention to provide a board element of the specified type which, in spite of a lower proportion of glass fiber reinforced polyester resin, will be stronger and retain its form better than known boards.